A patient suffering from spinal cord injury, encephalorrhagia or encephalomalacia, a patient after an operation or a bedridden old man is liable to show symptoms of dysuria, urine incontinence and the like. In such a case, a urethral catheter has been widely used for ensuring a smooth urinary passage and maintaining or improving the kidney function, or preventing the leakage of urine. However, in the case of a continuous drainage method wherein the urethral catheter is embedded in the body for a long period of time, the bladder is always contracted with the result that the normal drainage function obtained from a repetition of expansion and contraction is not possible. Generally, man has the following drainage mechanism; storing urine in the bladder, stimulating an inherent receptor in the bladder wall by expansion of the bladder wall due to repletion with urine, stimulating the drainage center of the cerebrum from the myelon through the brain stem which causes contraction of the bladder wall, relaxing the muscle group of the pelvis bottom, relaxing the urethral sphincter muscle and urinating. On the other hand, the drainage mechanism is prevented in a patient having a catheter embedded in the bladder, since the most essential process in the drainage mechanism, i.e. the repletion with urine and the stimulation of the receptor with the expansion of the bladder wall, is lost. In other words, the function of the bladder is completely stopped and the bladder becomes a passage for urine or a collecting space of urine. In such a case, there are medical and physiological problems which have been discussed for a long period of time. Three of these problems can be summarized as follows: First, since a patient is laid on one's back and the lowest point of the bladder becomes a dead space which gathers a small amount of residual urine, which, in turn, becomes a good culture medium for microbes which intrude into the bladder from inside or outside of the catheter tube, the bladder is a source of cystitis, pyelitis or pyelonephritis. Second since a tip of the ballon catheter inserted into the bladder always presses on a part of the contracted bladder wall, which results in an ulcer due to a poor circulation of the blood and then a necrosis which is known as "Foley tip necrosis", the diseased tissue becomes a suitable entrance for microbes, which may very likely cause cystitis to develop. Third, since the bladder function is completely prevented by use of the catheter, recovery of the bladder function becomes more delayed after prolonged use of the catheter. In the case of a patient suffering from ischuria after an operation on a pelvis, a spinal cord injury or a cerebrum blood vessel disease, it should be noted that the patient having used the embedded catheter for a long period of time has difficulty in training the bladder, even though training of the bladder is usually started in the subacute period (a recovering period of the drainage function).
In order to solve the above problems associated with the long-term indwelling of the catheter, U.S. Pat. Nos. 3,503,401 and 4,084,593 proposed a drainage control system and a bladder training apparatus, respectively, in which outlets of the urethral catheter are connected to a siphon. Since these apparatuses allow the bladder to alternately repeat expansion and contraction while the urethral catheter is embedded in the body, they seem to be useful for solving the above problems. However, problems still remain to be solved for a clinical use of these systems.
For example, the drainage control system described in U.S. Pat. No. 3,503,401 is an open system in which a drainage tube leading to a collection container from the urethral catheter is opened to the air. In this system, there is a period of transient pressure reduction in the drainage tube which arises right after siphoning, whereby a back flow can be produced from the air to the bladder. The back flow may be stronger than in the conventional continuous drainage method with the indwelling urethral catheter and may contain the microbes associated with dust in the air or from the polluted urine in the form of bubbles. There is a high probability that the invasion of microbes from the air to the bladder will cause an infection due to the microbes. Once the microbes invade the bladder they begin to proliferate exponentially in number. It would be more desirable, however, to reduce the number of microbes to as few as possible. Even though this system contemplates dilution and discharge of the microbes invaded into the bladder, there is no provision for preventing the invasion of the microbes, which is the major reason why the system is not practical for clinical use. This problem is also present where the invasion of microbes is from an air tube. A second problem is that a part forming the siphon tube is so thin and particularly so long that the liquid in the siphon tube can not be drained away completely and liquid columns are formed within the tube. In such a case, the siphon tube does not work well afterward. For example, if the air between two liquid columns is at low pressure, the siphon tube begins to work before the bladder fills up with urine.
In the bladder training apparatus to U.S. Pat. No. 4,084,593, the drainage cycle is very long in comparison with the usual drainage cycle. The intermittent autodrainage method accomplished by the above apparatus is superior to the conventional continuous drainage method in view of an anti-infection effect because the intermittent process completely drains urine away during a time in which the invaded microbes do not proliferate sufficiently. However, the microbes can proliferate enough to result in cystitis if the drainage cycle is long enough to store urine a sufficient length of time. Particularly, a serious illness such as pyelonephitis can be developed if during the intermittent drainage, the bladder is temporarily filled up. The above mentioned problem is knonw to persons in the medical field of urology and is described in MODERN MEDICINE, by Nishiura, December, page 22 (1979). It has been found that intervals of drainage should be done preferably within 3 hours, and at the most within 5 hours. However, in the bladder training apparatus of the above patent, a volume of a pressure chamber which is located below the bladder is larger than that of the bladder and a lower end of the inverse U-shaped siphon tube in the chamber is inserted close to the bottom of the chamber as shown in the specification, particularly in FIG. 1 and FIG. 2 (U.S. Pat. No. 4,084,593 does not disclose the relative sizes of the parts of the apparatus excepting the inside diameter of the siphon tube, but the disclosure does state that the relative location of the various components is as shown in the drawings). The amount of liquid to be drained by one siphoning, in other words, the amount of liquid to be filled before the next siphoning, is nearly equal to the total of the volume of the bladder (V.sub.1) and the volume of the above chamber above the lower end of the siphon tube (V.sub.2). The additional V.sub.2 which must be accommodated in the drain cycle causes the intervals of drainage to be longer than the usual cycle. From this point of view, it would be desirable to maintain the depth of the siphon tube of the above mentioned pressure chamber as shallow as possible. However, if the depth of the siphon tube is made shallow, the waste fluid above the lower end of the siphon tube will be drained away and the siphoning will be stopped before the whole content of the bladder is drained away due to the large flow-pressure loss which will occur in the thin inside diameter of the catheter. The above problem is difficult to solve due to the interdependency between V.sub.1, V.sub.2, the inside diameter of the catheter and the inside diameter of the siphon tube.
This problem is solved for the first time by the present invention in which a pressure control hole sealed by a filter having a property of restricting air flow is equipped with a pressure chamber, which is described hereinafter. On considering this point, a tube of the bladder training apparatus in U.S. Pat. No. 4,084,593 corresponding the air control tube of the present invention is connected to a collection container or an air-containing bag and therefore the air is free to flow, which can not solve the abovementioned problem. As described hereinbefore, the bladder training apparatus of U.S. Pat. No. 4,503,401 is useful for short term training of a bladder, but it is not suitable for long term training since it does not have a sufficient anti-infection capability to prevent infections from becoming started.
Also, U.S. Pat. Nos. 2,602,448 and 2,860,636 disclose a tidal drainage and an irrigating unit in which expansion and contraction of the bladder is alternately repeated according to the siphon principle. These apparatuses are different from the present invention in the following points.
Both apparatuses are bladder irrigating units, in which the irrigating mechanism comprises repetition of the following cycle; an irrigating agent flows into the inside of the apparatus and from a tube connected to the bottom of the apparatus through a catheter into a bladder, the inside pressure of the bladder rises and the liquid surface in the apparatus rises as the bladder is filling up with the agent and urine, and then when the liquid in the apparatus reaches a certain point the siphoning is begun and the content in the bladder is drained. Some differences between the apparatuses of the above U.S. Patents and the device of the present invention are that each apparatus has the inlet for the irrigating agent at the top of the apparatus and the connection inlet to the catheter is located below the lower end of the inlet of the outer siphon tube. If the connection inlet is located above the lower end of the outer siphon tube, air would flow into the bladder, which is undesirable in the operation of each apparatus of these U.S. Patents. On the other hand, in the apparatus of the present invention, a connecting nozzle connected to the catheter should be located above the lower end of the inlet of the siphon tube for achieving the following two objectives:
(1) so that no material flows into the bladder from the device; and
(2) so that residual urine in the bladder is decreased to as little as possible after siphoning.